Bacterial microbiota in small brown planthopper populations with different rice viruses

The small brown planthopper (Laodelphax striatellus) as a vector of the rice stripe virus

The small brown planthopper, Laodelphax striatellus, is a destructive pest insect found in rice fields. L. striatellus not only directly feeds on the phloem sap of rice but also transmits various viruses, such as rice stripe virus (RSV) and rice black-streaked dwarf virus, resulting in serious loss of rice production. RSV is a rice-infecting virus that is found mainly in Korea, China, and Japan. To develop novel strategies to control L. striatellus and L. striatellus-transmitted viruses, various studies have been conducted, based on vector biology, interactions between vectors and pathogens, and omics, including transcriptomics, proteomics, and metabolomics. In this review, we discuss the roles of saliva proteins during phloem sap-sucking and virus transmission, the diversity and role of the microbial community in L. striatellus, the profile and molecular mechanisms of insecticide resistance, classification of L. striatellus-transmitted RSV, its host range and symptoms, its genome composition and roles of virus-derived proteins, its distribution, interactions with L. striatellus, and resistance and control, to suggest future directions for integrated pest management to control L. striatellus and L. striatellus-transmitted viruses.

An improved method to efficiently acquire rice black-streaked dwarf virus viruliferous small brown planthoppers

Accurate phenotypic identification is the basis of research for resistance genetics and rice breeding for resistance to RBSDV disease. Obtaining rice black-streaked dwarf virus (RBSDV) viruliferous small brown planthoppers (SBPHs) with high transmission efficiency is an essential part of accurate phenotypic identification. Here, through quantifying number of RBSDV copies in infected rice plants, optimizing times of SBPHs fed on RBSDV-infected rice plants and leaf stage of rice seedlings, a method to acquire an RBSDV-carrying SBPH population more efficiently was improved. The results showed that rate of viruliferous SBPHs was significantly higher when fed on RBSDV-infected rice plants that had the copy numbers of RBSDV S10 of 3.0*10⁴ and 1.1*10⁴ than 8.3*10². Therefore, it is more efficient for SBPHs to acquire the virus when fed on RBSDV-infected rice plants that have copy numbers of RBSDV S10 above 1.1*10⁴. The rate of viruliferous SBPHs were 50% and 54%, respectively, after the insects fed on RBSDV-infected rice plants for 7 and 9 days and being transferred to healthy rice seedlings for 5 and 3 days, which was significantly higher than those at other feeding times. The optimal inoculation leaf stage of rice seedlings was the 2-3-leaf stage (3 effective SBPHs per seedling for 72 h), but a high rate of viruliferous SBPHs may be suggested for inoculation of older rice seedlings.

Host-Plant Induced Shifts in Microbial Community Structure in Small Brown Planthopper, Laodelphax striatellus (Homoptera: Delphacidae)

Microbiome associated with insects play vital roles in host ecology and physiology. The small brown planthopper (SBPH), Laodelphax striatellus, is a polyphagous insect pest that caused enormous damage to a wide range of cereal crops. Previous studies have assessed the effects of environmental factors, such as antibiotics, insecticide, and geographical habitat on the bacterial composition of SBPH. However, the influence of host plants on the microbial community in SBPH still unclear. Here, we characterized and compared the microbial community in three SBPH populations feeding on rice, barley, and wheat, respectively, using high-throughput amplicon sequencing. Our observations revealed that the microbiome harbored by SBPH was abundant and diverse. Ten phyla comprising 141 genera of bacteria were annotated, and four fungal phyla consisting of 47 genera were assigned. The bacteria belonging to the phylum Proteobacteria were the most prevalent and the fungi with the highest abundance were from the order Hypocreales. Comparative analysis showed that host plants could significantly induce structural changes of SBPH microbiome. Significant differences in abundance were observed in two main bacterial orders (Rickettsiales and Rhodospirillales) and three fungal classes (Sordariomycetes, an unclassified class in Ascomycota and Eurotiomycetes) among three host-adapted SBPH populations. Our results could broaden our understanding of interactions among SBPH, its microbial associates and host plants, and also represented the basis of future SBPH biological management.

Plant-Mediated Horizontal Transmission of Asaia Between White-Backed Planthoppers, Sogatella furcifera

Asaia is a bacterial symbiont of sugar-feeding insects that has been shown to be vertically transmitted by maternal transmission and paternal transmission mechanism, and to be horizontally transmitted via co-feeding artificial diet and venereal routes. Here, the first case of plant-mediated horizontal transmission of Asaia between white-backed planthoppers (WBPH), Sogatella furcifera, was reported. In Asaia-infected WBPH, Asaia was detected mostly in salivary glands and to a less extent in stylets. The rice leaf sheaths fed by Asaia-infected WBPH for 12 h were all positive with Asaia, where Asaia persisted for at least 30 d but was localized in the feeding sites only. When confined to Asaia-infected leaf sheaths for 7 d at the sites pre-infested by the Asaia-infected WBPH, all Asaia-free WBPH became infected with Asaia and the acquired Asaia could be vertically transmitted to their offspring. Phylogenetic analysis confirmed an identical Asaia strain in the Asaia-infected donor WBPH, the Asaia-infected leaf sheaths, and the newly infected recipient WBPH. Our findings provide direct evidence for the first time that rice plant can mediate horizontal transmission of Asaia between WBPH, which may contribute to the spread of Asaia in the field WBPH populations.

Similarities and spatial variations of bacterial and fungal communities in field rice planthopper (Hemiptera: Delphacidae) populations

Rice planthoppers are notorious plant sap-feeding pests which cause serious damage. While several microbes in rice planthoppers have been broadly characterized, the abundance and diversity of bacteria and fungi in field planthoppers are largely unknown. This study investigated the bacterial and fungal community compositions of Chinese wild rice planthoppers Laodelphax striatellus and Sogatella furcifera using parallel 16S rRNA gene amplicon and internal transcribed space region sequencing. The bacteria varied significantly between the species and were partitioned significantly by sex, tissues and host environments in each species. The majority of bacteria were affiliated with the genera Wolbachia, Cardinium, Rickettsia and Pantoea. The abundance of Wolbachia was negatively correlated with that of Cardinium in both planthopper species. Compared with bacteria, the abundance and diversity of fungi did not differ between sexes but both were enriched in the gut. The bacterial community as a whole showed no significant correlation with the fungal community. The majority of fungi were related to Sarocladium, Alternaria, Malassezia, Aspergillus and Curvularia. A phylogenetic analysis revealed that these fungi were closely related to botanic symbionts or pathogens. Our results provide novel insights into the bacteria and fungi of rice planthoppers.

Recent infection by Wolbachia alters microbial communities in wild Laodelphax striatellus populations

BACKGROUND

Host-associated microbial communities play an important role in the fitness of insect hosts. However, the factors shaping microbial communities in wild populations, including genetic background, ecological factors, and interactions among microbial species, remain largely unknown.

RESULTS

Here, we surveyed microbial communities of the small brown planthopper (SBPH, Laodelphax striatellus) across 17 geographical populations in China and Japan by using 16S rRNA amplicon sequencing. Using structural equation models (SEM) and Mantel analyses, we show that variation in microbial community structure is likely associated with longitude, annual mean precipitation (Bio12), and mitochondrial DNA variation. However, a Wolbachia infection, which is spreading to northern populations of SBPH, seems to have a relatively greater role than abiotic factors in shaping microbial community structure, leading to sharp decreases in bacterial taxon diversity and abundance in host-associated microbial communities. Comparative RNA-Seq analyses between Wolbachia-infected and -uninfected strains indicate that the Wolbachia do not seem to alter the immune reaction of SBPH, although Wolbachia affected expression of metabolism genes.

CONCLUSION

Together, our results identify potential factors and interactions among different microbial species in the microbial communities of SBPH, which can have effects on insect physiology, ecology, and evolution. Video Abstract.

Diversity, Tissue Localization, and Infection Pattern of Bacterial Symbionts of the White-Backed Planthopper, Sogatella furcifera (Hemiptera: Delphacidae)

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth), is a destructive pest of rice. Bacterial symbionts play an important role in insect hosts, especially hemipteran hosts. This study was designed to examine the bacterial symbionts of the WBPH using 16S rDNA high-throughput sequencing. A total of 63 and 177 operational taxonomic units (OTUs) were identified in females and males of three WBPH populations, respectively. These OTUs included bacteria of 75 genera from 11 phyla, where Wolbachia, Cardinium, and Asaia were the dominant genera, accounting for over 97.99% of all the symbiotic bacteria. Fluorescence in situ hybridization detected Wolbachia, Cardinium, and Asaia in the salivary glands, guts, testes, and eggs of the WBPH, indicating the potential for both horizontal and vertical transmission. Moreover, the infection pattern of the three dominant bacterial symbionts was detected in six WBPH populations. The frequencies of Wolbachia infection of females and Cardinium infection of both sexes were over 96.7%. Wolbachia infection of males ranged between 46.7 and 63.3%, which was significantly lower than that observed for females. Asaia infection of both sexes varied substantially among the populations. These results indicate that the complex host-symbiotic bacteria interaction is influenced by host sex and geographical origin and potentially by the transmission modes of the symbionts.

Characterization of a Bacterial Symbiont Asaia sp. in the White-Backed Planthopper, Sogatella furcifera, and Its Effects on Host Fitness

The white-backed planthopper (WBPH), Sogatella furcifera Horváth (Hemiptera: Delphacidae), is an economically significant rice insect pest that harbors a primary fungal yeast-like symbiont (YLS), and some secondary bacterial symbionts like Wolbachia and Cardinium. In the present study, an additional bacterial symbiont in WBPH was characterized. Phylogenetic analysis employing the 16S rRNA gene showed a bacterium closely related to Asaia of Nilaparvata lugens and Nysius expressus, and Asaia krungthepensis. TEM observation of the bacterium showed the typical morphology of Asaia sp. with signature filamentous structures in the nucleoid region. These results indicate that the bacterium belongs to Asaia. The Asaia bacterium was detected in all the tested individual adults and tissues of the laboratory WBPH population but showed varying infection rates (ca 45%) in the field collected WBPH populations. Quantitative PCR analysis revealed that Asaia sp. were significantly more abundant in WBPH females than males, and mainly distributed in the guts, fatty bodies, and salivary glands. Asaia-infected WBPH were of shorter nymphal duration and heavier adult weight than Asaia-free WBPH, while Asaia-free WBPH comparatively fed more, indicating that Asaia plays a role in improving WBPH fitness through involvement in host's nutrient supply.

Bacterial reproductive manipulators in rice planthoppers

Rice planthoppers (Hemiptera: Delphacidae) are notorious pests for rice (Oryza sativa) in Asia, posing a serious threat to rice production and grain security. Rice planthoppers harbor diverse bacterial symbionts, including Wolbachia, Cardinium, Spiroplasma, and Arsenophonus, which are known to manipulate reproduction in arthropod hosts. This microreview is to introduce current knowledge of bacterial reproductive manipulators in rice planthoppers, including their diversity, population dynamics, localization, transmission, and biological functions.

Honeydew-associated microbes elicit defense responses against brown planthopper in rice

Feeding of sucking insects, such as the rice brown planthopper (Nilaparvata lugens; BPH), causes only limited mechanical damage on plants that is otherwise essential for injury-triggered defense responses against herbivores. In pursuit of complementary BPH elicitors perceived by plants, we examined the potential effects of BPH honeydew secretions on the BPH monocot host, rice (Oryza sativa). We found that BPH honeydew strongly elicits direct and putative indirect defenses in rice, namely accumulation of phytoalexins in the leaves, and release of volatile organic compounds from the leaves that serve to attract natural enemies of herbivores, respectively. We then examined the elicitor active components in the honeydew and found that bacteria in the secretions are responsible for the activation of plant defense. Corroborating the importance of honeydew-associated microbiota for induced plant resistance, BPHs partially devoid of their microbiota via prolonged antibiotics ingestion induced significantly less defense in rice relative to antibiotic-free insects applied to similar groups of plants. Our data suggest that rice plants may additionally perceive herbivores via their honeydew-associated microbes, allowing them to discriminate between incompatible herbivores-that do not produce honeydew-and those that are compatible and therefore dangerous.